It would help woman keep track of body temperature to predict when women could become pregnant when not using traditional forms of birth control, the Evening Standard reported. It was promoted as an alternative to birth control pills and researchers believed in the results after they found it was up to 99 percent effective, the newspaper reported last year.

The app is popular in Europe where users went from 5,000 in 2016 to 125,000 in 2017.

And while there have been reports of unplanned pregnancies, the company markets Natural Cycles told the Daily Mail, “No contraception is 100 percent and unwanted pregnancies is an unfortunate risk with any contraception.”

Company officials said that the number that the hospital was reporting, 37 unplanned pregnancies out of 668 users, is within the 93 percent risk communicated to consumers, the Daily Mail reported.